Cobalt Containing Polyimide Films Treated by Nanosecond Pulsed Electrical Discharges in Water

This paper describes the effect of nanosecond pulsed electrical discharges generated in distilled water on cobalt-modified fluorinated polyimide (PI) films derived from hexafluoroisopropylidendiphthalic dianhydride and 4,4'-diamino-3,3'-dimethyl diphenylmethane. The PI films have been characterized by dielectric spectroscopy, X-ray photoelectron spectroscopy, and X-ray diffraction (XRD) measurements. The relative permittivity of the PI films increased after treatment by water plasma. The XRD analysis has shown a slight increase of the degree of intermolecular ordering and stronger π-π interactions with the increase of the plasma treatment time. Application of nanosecond high-voltage pulses has induced an increase in concentration of CF₃ groups at the polymer surface. A decrease of the cobalt and chlorine fractions, due to their migration into water, and an increase of aliphatic C-C bonds at the film surface may be responsible for the relative permittivity modification after exposure to water plasma.